Induction excitation of electric discharge tubes



March 7, 1939.

J. BETHENOD 2,149,414

INDUCTION EXCITATION OF ELECTRIC DISCHARGE TUBES Filed Oct. 14, 1935M/VZWUR Jose 0A 5e [AenocZ ATTORNEY .5 sage through the coil of aPatented Mar. 7, 1939 PATENT OFFICE In ut-non axons-non or sworn-1cDrscnAB E roses Joseph Bethenod, Paris, France, assignor to SocietAnonyme pour les Applications de l'Electrloit et des Gas Bares Pas aSilva. a Won Etablissemcnts Claudeof France Application October 14,1935, Serial No. 44,983

In France October 1 1 ClallIL- (Cl. 116-124) The present inventionrelates to a method of feeding tubes for electrical discharge in gases vby means of a source of periodic current of high frequency, for example,by means of a high fre- 5 quency-alternator. Thissource of current has aconstant voltage during the whole period of ous medium of the tube forducing and maintaining in this gaseous medium a discherse with sparkspectrum. invention and the claim includ .the case in which, in such aninstallation, the prolonged pascurrent corresponding to starting currentfor thi the purpose of pros discharge would produce excessive heating ofthe coil, and it includes a means for avoiding this heating.

The case considered 20 frequency of the supply that which may beproduced industrially by a 7 high frequency alternate say about 30,000cycles per second. The considerable electric field to be induced in thegaseous; medium for the obtaining 05 of the said discharge is thenattained by bringing .the current through the coil to an extremely highvalue which, after the startins of the tube. remains so important as togive rise to said ex cessive heating. "3 According to the invention, theabove-mentioned means consists in tuning the circuit of the inductioncoil to resonance on the alternating current supply frequency to providesufficient potential on said coil to start a discharge in the gaseousmedium yielding a spark spectrum, the resonant circuit having a dampingcharacter such that the frequency shift, due to the changing impedanceof this circuit, operates to limit the current to a value between thatat which the 40 spark spectrum type of discharge would be inhibited andthat at which the heating of the coil would terminate the discharge.

In the accompanying drawing is shown, by way of example only, a singleflgure of a diagram in accordance with the present invention.

' The induction winding may comprise magnetic core (not showri), is 50high frequency alternator 3. A condenser l is connected in series withthe winding I and used for the tuning to rescue cc of the coil circuit.

a finely supplied by the The present while another condenser 5 isconnected across the terminal of the winding 1.

The current mrnished by the potential source is such that it wouldcorrespond to the operation of the tube-under arc s rum conditions-the 5damping produced by the gaseous medium then being small-had the coilcircuit not been brought to the frequency of the alternator.

Due to this tuning, the induction coil istraversed by an intense currentand the difference of 10 a considerable value to which there correspondsan electrostatic field suflicient to produce a high ionization of thegaseous medium. Therefore, the conductivity of the said medium is highlyincreased in such a manner that, by means of a suitable selection of thevarious constants, the s ark spectrum working conditions are fulfilledand the starting takes place. As soon as the starting its effected, thehigh reaction of the ionized medium on the induction winding reduces thecurrent to the permissible value whichcan be supported without danger tothis winding. Everything takes place then, as regards the dischargedevice I, 2, as if it were a transformer, the secondary load circuit ofwhich, constituted here by the gaseous medium, had been closed suddenly.

The invention covers numerous variations without departure from itsscope, as expressed in the appended claim. Thus, the condenser I may bedispensed with, the condenser 0 alone being connected in series with thewinding I.

I claim: I In combination, a gaseous dischars device having a gaseousmedium ductively coupled to the gaseous medium in said discharge devicethat a spark spectrum may be produced in said medium by energizing saidcoil, means for supplying alternating current to said coil comprisingtuning means adapted to conthe coil a circuit resonant to the supplyfrequency to provide suflicient potential on said coil to start adischarge the resonant circuit having a damping character such that thefrequency shift, due to the changing impedance of this circuit, operatesto limit the current to a value between that at which the spark spectrumtype of discharge would be inhibited and that at which the heating ofthe coil would terminate the discharge.

JOSEPH BETHENOD.

